The polyvinyl chloride resin has frequently been used in the field of transparent sheets. In association with the trend for higher awareness to the problems of environmental contaminations or the like in recent years, there is a strong need for development of a novel transparent sheet which can be used in place of the polyvinyl chloride resin sheet. As one of the sheets satisfying the requirement, recently a sheet made of polypropylene is often used. In the field of the sheets, there is a need for development of transparent sheets satisfying not only the requirement for transparency, but also the requirements for excellent physical properties, especially for higher impact resistance.
As a method of improving the impact resistance of a polypropylene sheet, there has been known, for instance, the following technologies.    (1) The quenching method using an HPP (homopolypropylene) resin composition with an ethylene-butene-1 copolymer with the low crystallinity blended therein (Japanese Patent Laid-Open Publication No. SHO 62-227722).    (2) The quenching method using an HPP resin composition with an ethylene-butene-1 copolymer with the low density and a nucleating agent blended therein. Especially, the method in which, as the PP, an RPP (random polypropylene) is blended in the HPP (Japanese Patent Laid-Open Publication No. HEI 1-306448).    (3) The quenching method using an HPP with an ethylene-propylene rubber and ethylene- α olefin copolymer blended therein.
Further as a method of improving the rigidity and transparency of a transparent polypropylene sheet, there has been known the following method.    (4) The method in which a transparentizing agent such as a nucleating agent or a petroleum resin is blended in a material for polypropylene.
In the methods (1), (2) and (3) described above, improvement of the impact resistance can be expected. However, the rigidity of the sheet lowers, and also the transparency is sacrificed. Further there occur such new problems as degradation of the transparency due to generation of a gel during recycled use of the sheet, poor appearance, lower adaptability for printing, and whitening during a bending process.
In the method (4) described above, there is the problem of lower impact resistance.